1. Technical Field
The present invention relates to a method of forming a through hole in a substrate.
2. Related Art
A MEMS (Micro Electro Mechanical Systems) device is a device which has anew function and in which a micro structure and an electric circuit are combined and are miniaturized. Hitherto, in the MEMS device, a microfabrication technology developed mainly in a semiconductor device manufacturing technology is applied, and a structure of several μm to several hundred μm is formed on a silicon substrate or the like, so that a passive device such as a sensor and an active device such as an actuator are formed. Through holes for forming the structures of the MEMS devices are formed by etching or the like so as not to break the silicon substrate or the like.
JP-A-2007-168344 (patent document 1) discloses a through hole forming method including a step of forming a continuous nozzle hole (through hole), which has a small-hole end closed by a base member and a large-diameter hole base end opening on a surface of the base member and has a two-stage shape, by an etching process in the silicon base member, a step of bonding a support substrate to the large-diameter hole side surface of the silicon base member, and a step of thinning the small-diameter hole side surface of the silicon base member to open the end part of the small-diameter hole.
In a through hole forming method disclosed in JP-A-2010-240852 (patent document 2), dry etching is performed from one surface side of a silicon substrate to form a recess which becomes a first nozzle part (through hole), a protecting film having etching resistance is formed on the whole of the one surface of the silicon substrate including an inner wall of the recess, and a support substrate is bonded to the one surface. In that state, the silicon substrate is thinned from the other surface side so as to have a desired thickness, and a second nozzle part (through hole) communicating with the first nozzle part is formed by performing dry etching from the other surface side so as to open the bottom of the recess which becomes the first nozzle part. A first protecting film remaining on a portion corresponding to the bottom of the recess, which becomes the first nozzle part, is removed, and the support substrate is removed from the silicon substrate.
However, in the patent document 1, since the formation of the through hole is performed from the one side of the substrate, there is a problem that the shape of the terminal part of the etched hole becomes thin as compared with the etching start point. In the patent document 2, there is a problem that if a plurality of recesses which become through holes having different opening areas are formed simultaneously, the depths of the formed recesses vary according to the opening areas, and the depths of the recesses cannot be controlled. Besides, there is also a problem that if the through hole having a large opening area is formed, the protecting film formed on the recess is damaged when the second nozzle part, which becomes the through hole opposite to the recess, is formed, and gas for cooling the heat generated by the etching leaks.
Accordingly, a through hole forming method is required in which in a substrate on which a MEMS device or the like is formed, the shape of a hole which becomes a through hole is uniform from the start point of etching to the terminal end, gas used for the etching does not leak, and depths of recesses which become through holes having different areas can be controlled.